1. Field of the Invention
The present invention is generally related to turbidity sensors and, more particularly, to a turbidity sensor that arranges a light source and two photosensitive devices in such a way as to permit easy removal and replacement of transparent covers with respect to the circuitry and components of the sensor wherein the covers, are attachable to a support structure.
2. Description of the Prior Art
Various types of turbidity sensors are known to those skilled in the art. Turbidity sensors have been used in appliances, such as dishwashers, to monitor the turbidity of the wash fluid during the washing process. U.S. Pat. No. 5,446,531, which issued to Boyer et al on Aug. 29, 1995, describes a sensor platform for use in machines for washing articles. A plurality of fluid condition sensors are combined together to provide a sensor cluster that senses turbidity, temperature, conductivity and the movement of a ferromagnetic object. The plurality of sensors are attached to a substrate and encapsulated, by an overmolding process, with a light transmissive and fluid impermeable material. The sensor cluster can be disposed at numerous different locations within a body of fluid and does not require a conduit to direct the fluid to a particular location proximate the sensor. In a preferred embodiment of invention, a circuit is provided which monitors the signal strength of first and second light sensitive components to determine turbidity and, in addition, those signals strengths are also used to advantageously determine the most efficient magnitude of current necessary to drive a light source, such as a light emitting diode. By controlling the current to a light emitting diode as a function of the strength of light signal received by first and second light sensitive components, the turbidity sensor can be operated at a more efficient and effective level.
U.S. Pat. No. 5,444,531, which issued to Foreman et al on Aug. 22, 1995, discloses a sensor with LED current control for use in machines for washing articles. Similar to the basic structure of the turbidity sensor described in U.S. Pat. No. 5,446,531, this turbidity sensor controls the current flowing through a light emitting diode in response to signals received from two photosensitive components.
U.S. Pat. No. 5,485,013, which issued to Cummins on Jan. 16, 1996, discloses a turbidity sensor with a light aperture arrangement of two openings formed in two parallel plates. The turbidity sensor is provided with two plates which each have an aperture formed therethrough. The apertures are aligned to define a light passage from a light source such as a light emitting diode. By properly selecting the gap between the two plates and the size of the two apertures, the angle of divergence of light emanating from the light source can be controlled and reduced to a magnitude that prevents light from passing directly from the light source to a scattered light detector of the turbidity sensor. The arrangement avoids the necessity of using expensive focusing lens.
U.S. Pat. No. 5,291,626, which issued to Molnar et al on Mar. 8, 1994, discloses a machine for cleansing articles, such as a dishwasher. The machine incorporates a device for measuring the turbidity of at least partially transparent liquid. The device includes a sensor for detecting scattered electromagnetic radiation, regardless of polarization, and a sense for detecting transmitted electromagnetic radiation, regardless of polarization.